1. Field of the Invention
The present invention generally relates to an integrated electric/electronic device, and, more particularly, to a hybrid integrated circuit device in which a connector lead is bonded by soldering or a like process to a conductor foil pattern deposited on a metallic circuit substrate having a high thermal conductivity.
2. Description of the Related Art
For better understanding of the invention, the background technique will first be described in some detail. FIG. 8 is a sectional view of a hybrid integrated circuit device known heretofore. Referring to the figure, there is mounted on one surface of a heat sink 1 of aluminum having an approximately U-like vertical section a metallic substrate 3 having a high thermal conductivity. More specifically, the metallic circuit substrate 3 is composed of a metal base 5 formed of aluminum, iron, silicon-steel sheet or the like and having a high thermal conductivity and an insulation layer 7 on the metal base 5, wherein a plurality of conductor foil patterns 9 are located on the insulation layer 7. The insulation layer 7 is made an adhesive epoxy resin filled with an inorganic filler.
A connector 11 is provided at one end of the aluminum heat sink 1. Extending from the connector 11 is a connector lead 13 which has a tip end bonded to one of the conductor foil patterns 9 on the insulation layer 7 with solder 15, while a heat sink 17 of copper is bonded to another one of the conductor foil patterns 9 with solder 19, and the semiconductor device 21 is bonded to the copper heat sink 17 with solder 23. The semiconductor device 21 is connected to another one of the conductor foil patterns 9 by means of a wire 25 of aluminum.
To manufacture the hybrid integrated circuit device known heretofore, solder paste is applied to the conductor foil patterns 9 deposited on the metallic circuit substrate 3, whereon a subassembly of the copper heat sink 17 and the semiconductor device 21 bonded together in a soldering furnace is placed on the solder paste. After securing together the subassembly of the copper heat sink 17 and the semiconductor device 21 by reflowing the solder, the semiconductor device 21 and the conductor foil patterns 9 are electrically interconnected by bonding the aluminum wire 25 thereto. Subsequently, the connector lead 13 is soldered to one of the conductor foil patterns 9 electrically connecting the lead 13 to the conductor foil patterns 9.
The hybrid integrated circuit device known heretofore suffers a problem that because of the high heat capacities of the metallic circuit substrate 3 and the connector lead 13, heat tends to be dissipated upon bonding of the connector lead 13 to the conductor foil pattern 9 by soldering, resulting in solder bonding which is poor in mechanical strength and reliability even though electrical connection can be ensured.